Exemplary embodiments of the present invention relate to a technology for fabricating a semiconductor device, and more particularly, to a resistance changing device and a fabrication method thereof.
Recently, researchers have been seeking to develop the next-generation memory devices that can replace Dynamic Random Access Memory (DRAM) devices and flash memory devices. Among the next-generation memory devices is a resistive memory device, such as Resistive Random Access Memory (ReRAM) employing a resistance changing device, which rapidly changes a resistance by performing a switching operation between two different resistance states based on an applied voltage.
FIG. 1 is a cross-sectional view illustrating a conventional resistance changing device. Referring to FIG. 1, the conventional resistance changing device includes a lower electrode 11, a resistive layer 13, and an upper electrode 12 sequentially stacked therein. The resistive layer 13 is typically formed of a metal oxide, which includes vacancies inside (e.g., oxygen vacancies).
The resistance changing device, including the lower electrode 11, the resistive layer 13, and the upper electrode 12 sequentially stacked, changes a resistance value by controlling a current and a voltage through a forming process where a predetermined voltage is applied to the lower and upper electrodes 11 and 12. In short, the resistance changing device operates through the forming process.
The switching mechanism of the resistance changing device having the above-described structure will be briefly described herein.
When a bias is applied to the lower and upper electrodes 11 and 12, conductive filaments may be generated through a rearrangement of vacancies in the resistive layer 13 or the vacancies are and, as a result, the conductive filaments generated before are removed based on the applied bias. The resistive layer 13 can represent the two resistance states distinguished by the generation or removal of the conductive filaments in the resistive layer 13. In other words, when the conductive filaments are generated, the resistance changing device represents a low resistance state, and when the conductive filaments are removed, the resistance changing device represents a high resistance state. Herein, an operation for generating the conductive filaments in the resistive layer 13, so that the resistive layer 13 represents the low resistance state is called a set operation. Conversely, an operation for removing the conductive filaments in the resistive layer 13, so that the resistive layer 13 represents the high resistance state is called a reset operation.
However, the conventional technology employing the resistive layer 13 formed of a metal oxide typically has a high reset current magnitude. This causes concern regarding an increase in power consumption of a resistive memory device employing the resistance changing device.
Also, although the resistance changing device generates or removes the conductive filaments through a rearrangement of the vacancies in the resistive layer 13, the resistance changing device hardly forms the vacancies, which are lattice defects, in a uniform distribution in the resistive layer 13. Therefore, there is concern that the distributions of set/reset voltage and set/reset current are not uniform in the resistance changing device. This deteriorates the operation characteristics and reliability of the resistive memory device employing the resistance changing device.